兩階段鋰離子電芯主動式平衡

Two Stage Active Balance Method for Lithium Ion Cells in Series

電動船業界克服串聯鋰離子電池芯不一致性主要在串聯電池模組內使用被動電阻式放電方法解決鋰鐵電池組電壓不平衡的問題，也有少部份的業者使用不同型式的主動式平衡，但不管是被動式或主動式平衡都有充電時單電芯過充或無法有效充飽電池組的缺點。本文提出一個全新的二階段主動式平衡電路改善現存平衡電路的不足。本二階段主動式平衡系統是在對鋰離子電池組充電時使用一創新的選擇電路對每個電池電芯電壓等值化；系統自動找出電池組中電芯的最小電壓，並將此最小電壓電芯的電壓拉抬至設定值，之後系統會反覆將當時具最小電壓電芯拉到設定值，當任一電芯的電壓達到過充的條件後，本平衡系統會轉入分充模式，依序用定電壓的方式將每一串聯的單電芯分充至飽電，藉此兩階段充電方式達到充電時絕不過充且每一電芯皆可達到飽電狀態。本文使用一組16顆鋰鐵磷電池芯串連而成的48V電池組，測試所開發的二階段主動式平衡系統，詳細紀錄此電池組在不同充放電電流的過程，實際測試結果顯示本二階段主動式平衡系統可在電芯不過充的限制下快速達成均充的狀態。 Passive dissipation cell balance via selective switches and resistors is predominantly used in the EV industry to overcome inconsistency problem commonly existed in lithium ion cells. Some use active schemes with various intermediate storage elements to enhance cell balance efficiency. However both balance methods suffer the setbacks of unavoidable cell overcharging or insufficient charge. The current study therefore developed a two-staged charging scheme to balance cell inconsistency without the shortcomings of existing balance methods. The newly developed two-staged charging scheme used an innovative switch matrix to select and equalize cell voltages in a lithium ion battery module. Our system automatically selected the cell with the minimum voltage and raised the voltage of this cell with balance current until a preset voltage condition was reached. Then the system would continue to raise the next cell with the minimum voltage until any overcharged condition was reached in any cell. The system would turn to the second charging stage, charging each cell with a constant voltage mode until a preset voltage level was reached. The second charging stage charged each cell respectively until each cell reached fully charged state while no single cell would be overcharged by any chance. A 48V/16S lithium iron module was adopted to lest the developed two-staged charging balance scheme. Detailed charging and discharging processes were recorded and analyzed. Experimental results showed the current balance method can rapidly reach cell balance state without suffering any cell over charge.